1. Field
The present disclosure relates generally to telecommunications, and more particularly, to a wideband phase modulator.
2. Background
Modern telecommunication systems are designed to allow a transmitter to communicate with a receiver over a transmission medium by modulating a carrier signal. Numerous modulation techniques are known in the art, such as amplitude modulation, frequency modulation, and phase modulation. These modulation schemes may be used to convey information by varying some aspect of a carrier signal.
A constellation diagram is commonly used to represent a carrier signal modulated with digital information. The constellation diagram is a two-dimensional scatter diagram of constellation points in the complex plane, with each constellation point representing a modulation symbol. Each modulation symbol in the constellation diagram has a real and imaginary component. The real component is referred to as the in-phase (I) component and the imaginary component is referred to as the quadrature phase (Q) component. By modulating a cosine carrier with the I component of the modulation symbol and a sine carrier with the Q component of the modulation symbol, the symbol can be transmitted with two carrier signals at the same frequency, which can be independently demodulated at the receiver. The concept of using two independently modulated signal carriers is known as quadrature modulation.
Another common modulation technique is known as polar modulation. In contrast to quadrature modulation, which represents each modulation symbol in the constellation diagram by its I and Q components, polar modulation represents each symbol by its polar coordinates. More precisely, each modulation symbol in the constellation diagram can be represented by two polar components: the radial component and the angular component. The radial component is used to modulate the amplitude of the carrier signal and the angular component is used to modulate the phase.
In polar modulation systems, a phase locked loop (PLL) is commonly employed to modulate the phase of the carrier signal. Unfortunately, the PLL is limited to narrowband applications. With the recent emergence of wideband technologies to support short range communications in dense multipath environments, PLLs may no longer be a viable option. Accordingly, there is a need in the art for improved methods to modulate the phase of a carrier signal for wideband applications.